1. Field of the Invention
The present invention relates to a vibration actuator which vibrates to generate a relative movement between a vibration element and a relative moving member. More particularly, the present invention relates to a vibration actuator having a supporting member including a plurality of position determining members to support a vibration member for stable vibration.
2. Description of the Related Art
Various vibration actuators are known, such as ultrasonic motors, which have characteristics, such as high torque, good controllability, high sustaining power, and noiselessness. For example, one well known type of vibration actuator is "a longitudinal L1-bending B4 mode flat-plate motor," which is described in "222 Piezoelectric Linear Motors for Application to Driving a Light Pick-Up Element, 5th Symposium on Dynamics Related to Electro-magnetic Force, Collected Papers." The known vibration actuator produces an elliptical motion by generating a first order longitudinal vibration, as well as a fourth order bending vibration, thereby generating a driving force through the elliptical motion.
FIG. 14 is a perspective view of an example of a known standing wave type vibration actuator that produces an elliptical motion by generating longitudinal vibration and bending vibration. As shown in FIG. 14, the vibration actuator 120 consists of an elastic member 121; a piezoelectric member 122, which is an electromechanical converting element connected to one of the planes of the elastic member 121; a relative moving member 123 in contact with driving force output members 121b and 121c provided on the other plane of the elastic member 121; and a supporting member 124 to control the position of the elastic member 121.
The elastic member 121 consists of a flat-plate type base 121a, and driving force output members 121b and 121c provided as protrusions on the lower side of the base 121a in order to transmit the driving force. The driving force output members 121b and 121c are provided at the antinode portion (the area where the amplitude is at its maximum) of the bending vibration that occurs during the drive function.
Piezoelectric member 122 is an electromechanical converting element to convert an electrical signal to a mechanical displacement. The piezoelectric member 122 includes driving piezoelectric members 122a and 122b, as well as vibration monitoring piezoelectric members 122p and 122p'. Piezoelectric members 122a, 122b, 122p and 122p' are adhered onto the upper surface of the elastic member 121.
Engaging grooves 121d and 121e are provided on each side of a central area in the width dimension of the base 121a of the elastic member 121, and have a semi-circular configuration when cross-sectioned. The engaging grooves 121d and 121e penetrate through the thickness of the base of 121a and piezoelectric members 122a and 122b.
The supporting member 124 consists of engaging parts 124b and 124c on each side of the bottom surface of the rectangular flat plate supporting member main body 124a disposed at an interval equal to that of engaging grooves 121d and 121e provided on elastic member 121. Engaging part 124b fits in engaging groove 121d, while engaging part 124c fits in engaging groove 121e. In accordance with the structure shown in FIG. 14, the supporting member 124 engages the elastic member 121 from the side where the piezoelectric element 122 of the elastic member 121 is provided. As a result, the supporting member 124 restricts the position of the elastic member 121 in terms of the width direction of elastic member 121, which is a direction that intersects the direction of the relative movement of elastic member 121 (in a direction indicted by the bidirectional arrow in the FIG. 14).
In accordance with the configuration shown in FIG. 14, when a first alternating voltage is applied to the driving piezoelectric member 122a and another alternating voltage having a phase electrically 90 degrees different from that of the first alternating voltage is applied to the driving piezoelectric member 122b, both longitudinal and bending vibrations occur in the elastic member 121. An elliptical movement, synthesized from the longitudinal and bending vibrations, occurs on the driving force output members 121b and 121c, thereby producing a driving force through the elliptical movement to create a relative movement between the elastic member 121 and relative moving member 123.
The vibration monitoring piezoelectric members 122p and 122p' are mechano-electro converting elements. The vibration monitoring piezoelectric members 122p and 122p' generate signals according to the state of the vibrations generated on elastic member 121 and send these signals to a drive circuit (not shown in the figure). Furthermore, the elastic member 121 is connected to a GND potential (not shown in the figure).
However, with the structure shown in FIG. 14, since the engaging parts 124b and 124c are designed to fit in engaging grooves 121d and 121e, respectively, provided on elastic member 121, it is inevitable that gaps are created between the engaging grooves 121d, 121e and the engaging parts 124b, 124c.
If, for example, the gap between the engaging grooves 121d, 121e and the engaging parts 124b, 124c is created along the direction of relative movement between the elastic member 121 and the relative movement member 123, then a backlash may occur at start up, or when reversing, and the vibration actuator 120 or elastic member 121 may shift back and forth when driven. Further, precision in determining a position decreases as a result of the unsteadiness caused by the gap between the engaging grooves 121 and the engaging parts 124 when starting or reversing the vibration actuator, thereby decreasing the capability for responsiveness as well. Still further, the engaging part 124 may collide with the inner wall of the engaging groove 121, or a yawing rotation of elastic member 121 may become unstable with respect to the direction of relative movement. Furthermore, as indicated by an arrow in FIG. 14, a rolling vibration may occur in the elastic member 121. The rolling vibration may result in a vibration and noise from the device in which vibration actuator 120 is integrated.
Moreover, if the gap is created across the direction of relative movement, the elastic member 121 may shift in either the left or right directions while the vibration actuator is driven, thereby resulting in vibration and noise of the device. These vibrations adversely affect the transmission of the driving force between driving force output members 121b and 121c and relative moving member 123, thereby resulting in a reduction of both the driving speed and the driving force. As a result, the driving efficiency of the vibration actuator decreases.